This invention relates to tetravalent organotin compounds, particularly organotin functionalized silanes, a solid prepared by chemically bonding the organotin functionalized silane to an inorganic support containing surface hydroxy groups; a catalyst prepared from said supported organotin functionalized silane; a continuous or batch process for conducting esterification, or transesterification reactions, and urethane, urea, silicone, or amino forming reactions utilizing said solid supported catalyst and the reaction products of such continuous or batch processes involving the separation of the solid tin-containing catalyst from the liquid reaction products to yield tin catalyzed product containing very low levels of tin.
Homogeneous organotin compounds are known to be effective catalysts for esterification, transesterification, siloxane, and urethane forming reactions by those skilled in the art. However, separation of the homogeneous organotin catalysts from the reaction products is a major disadvantage which is frequently not possible or requires special treatment that usually destroys the catalyst. Homogeneous catalysts are in the same phase, usually liquid, as the reactants and reaction products. Heterogeneous catalysts are of a different phase than the reaction products.
Many types of heterogeneous catalysts are known and have a number of significant advantages over homogeneous catalysts such as ease of separation of the catalyst from the reaction products facilitating re-use of the catalysts and high mechanical and thermal stability over a wide range of processing conditions. Heterogeneous catalysts are sometimes not as selective as homogeneous catalysts. Supported metal complexes, metal complexes attached to the support by a chemical bond, are often as selective as their homogeneous counterparts.
There are two types of supports for heterogeneous catalysts, polymeric and inorganic. Polymer supports are popular because they are easily functionalized and have a flexible structure facilitating interactions between active catalyst sites and reactants. Polymer supports though have several significant disadvantages such as poor mechanical properties, limited thermal stability typically below 160.degree. C., and a lack of physical rigidity over a wide range of processing conditions making control over the porosity and diffusional characteristics difficult.
Most known polymeric organotin compounds are not effective catalysts because of they do not possess the desired functionality for esterification; and transesterification reactopms, urethane, urea, silicone, and amino forming reactions or the fact that the tin tends to leach out too quickly from the polymer so that only a few reactions may be conducted. Jiang, et al in U.S. Pat. Nos. 5,436,357 and 5,561,205 have disclosed polymeric organotin compounds in which the organotin is attached to the polymer via a non-labile bond and found to be effective for transesterification reactions. However, the polymeric organotin compounds are limited to reactions temperatures in the range of 50 to 150.degree. C. and thus are not expected to be effective for esterification reactions, typically carried out at temperatures exceeding 200.degree. C. when homogeneous organotin catalysts are used.
Inorganic supports have a number of distinct advantages over polymer supports. They have a rigid structure which allows greater control over the porosity and diffusional characteristics of the support and are not affected by process conditions. The thermal stability is usually limited by the stability of the supported complex and not by the support itself. They also have high mechanical stability that prevents physical breakdown of the particle and the formation of "fines." Metal oxides are the most frequently used inorganic support owing to the fact that metal oxides contain surface hydroxyl groups which can be readily functionalized. Two modes of attachment are generally used for supporting complexes on the surface of metal oxides. The first is through the use of a metal complex that contains a labile ligand capable of reacting with the surface hydroxy groups to give a reaction product in which the metal center in the complex is directly bonded to the surface through an oxygen atom. EQU {E}--OH+X--M.fwdarw.{E}--O--M+HX
where
{E}--OH=metal oxide PA1 M=metal center in the complex PA1 X=labile ligand PA1 {E}--OH=metal oxide PA1 X=MeO, EtO,Cl, . . . PA1 Y=functional group
Typically, the preferred mode of attachment of the metal complex is through the use of a functionalized silane that contains labile ligands on the silicon capable of reacting with the surface hydroxy groups of the metal oxide support such as EQU {E}--OH+X.sub.3 SiY.fwdarw.{E}O--SiY
where
Leaching of the metal complex from the surface can be serious if there is any degree of dissociation of the metal under reaction conditions.
Most known organotin compounds are not suitable for preparing the heterogeneous catalysts of this invention because they either do not have the desired functionality for esterification, transesterification, and urethane, urea, silicone, and amino forming reactions, cannot be modified to contain such functionality, or do not form stable bonds with inorganic supports. The synthesis of several silylmethyltin trichlorides and bis(silylmethyl)tin dichlorides have been reported by Mironov, V. F., Stepina, E. M., and Shiryaev, E. M., Zh. Obshch Khim., 42 631 (1972); Mironov, V. F., Shiryaev, E. M., Yankov, V. V., Gladchenko, A. F. and Naumov, A. D., Zh. Obshch Khim., 44, 806 (1974); Mironov, V. F., Shiryaev, V. I., Stepina, E. M., Yankov, V. V., and Kochergin, V. P., Zh. Obshch Khim., 45, 2448 (1975), but do not disclose or suggest bonding these compounds to an inorganic support nor have they determined their effectiveness as catalysts. Similarly, Auner, N. and Grobe J., Z. Anorg. Allg. Chem. 500, 132 (1983) reported a number of 3-silylpropyltin trichlorides but do not disclose or suggest bonding these compounds to an inorganic support and have not determined their effectiveness as catalysts. Schumann, H and Pachaly, B., Angew. Chem. Int. Ed. Engl., 20, 1043 (1981); Schumann, H., and Pachaly, B., J. Organometal. Chem., 233, 281 (1982); Schumann, H., and Pachaly, B., Ger. Offen. 3116643, disclosed several organotin compounds that were supported on alumina and silica, however, they either do not contain the desired functionality for catalysis or there is a labile bond between the silicon and the tin. Matlin, S. A. and Gandharn, P. S., J. Chem. Soc., Chem. Commun., 798 (1984) reported the use of an organotin dimethoxide linked to the surface of silica that is effective as a hydride transfer catalyst for the reduction of ketones and aldehydes.
It is the object of this invention therefore, to produce organotin functionalized silanes wherein the organotin is linked to the silane by a stable ligand group(non-labile at both the tin and silicon ends), at least one of the ligands on the silane end of the molecule is labile and results in a stable silicon oxygen bond with the surface of the inorganic supports, and at least one of the ligands on the tin end of the molecule is a labile group.
Another object of this invention is to prepare a solid comprising an organotin functionalized silane on an inorganic support, which is useful in preparing a transesterification, esterification, or urethane forming catalyst.
A further object of this invention is to prepare a heterogeneous catalyst for transesterification, esterification, or urethane, urea, silicone, and amino forming reactions which has high selectivity, high activity and long catalyst life.
Yet another object of this invention is to provide a process for conducting transesterification, esterification, and urethane, urea, silicone, and amino forming reactions.